1. Field of Invention
This invention relates generally to the field of methods and apparatus for treating patients with brain and heart ischemia by rapid induction of hypothermia. More specifically, this invention relates to devices for rapid induction of brain and heart hypothermia during cardiac arrest.
2. Background Art
Mild hypothermia is recommended for out-of-hospital arrest patients where the initial rhythm was ventricular fibrillation (VF). Mild hypothermia (32-34° C.) has been shown to improve the outcomes of cardiac arrest, stroke, brain trauma, acute myocardial infarct and more. Recent studies suggest that hypothermia should be induced early and quickly.
A variety of methods demonstrated the ability to cool the brain and heart. Most commonly, external cooling by means of ice bags or chilling blankets is used. Other external devices such as a head cover were described to cool primarily the head.
Invasive, endocorporeal cooling of blood is described in U.S. Pat. No. 6,726,710 B2 and U.S. Pat. No. 6,849,083 B2. These patents describe whole body cooling by cooling the blood via a heat exchanger placed in a catheter inserted to the vena cava.
Cardiopulmonary bypass is used routinely to cool the heart. Several methods, based on bypass configuration, were demonstrated to rapidly cool the brain. More recently, methods of cooling through two veins were described. Furse et al. teach delivering cold saline to the brain via cannulation of vertebral artery after occlusion of the bilateral common carotid and the left vertebral arteries and drainage of excess fluid via microfiltration probe in the cortices. [M. Furuse, T. Ohta, T. Ikenaga, Y. M. Liang, N. Isono, T. Kuroiwa, and M. C. Preul, “Effects of intravascular perfusion of cooled crystalloid solution on cold-induced brain injury using an extracorporeal cooling-filtration system,” Acta Neurochirurgica, vol. 145, pp. 983-993, 2003.] Behringer et al. teach cooling by circulating blood between to two venous accesses through a heat exchanger. However, none of the prior art describes a system that uses only one venous access to extracorporeally cool blood. [W. Behringer, P. Safar, X. Wu, A. Nozari, A. Abdullah, S. W. Stezoski, and S. A. Tisherman, “Veno-venous extracorporeal blood shunt cooling to induce mild hypothermia in dog experiments and review of cooling methods,” Resuscitation, vol. 54, pp. 89-98, 2002.].
Several methods and apparati for withdrawal and infusion of blood have been described. Blood withdrawal pump controllers are described in U.S. Pat. Nos. 5,536,237, 4,657,529 and 6,585,675. The authors of U.S. Pat. Nos. 5,536,237 and 4,657,529 adjust the rate of withdrawal by using a relationship between flow and pressure established via a calibration curve. These authors do not provide a solution for vessel collapse during withdrawal except removal of the needle. U.S. Pat. No. 6,585,675 teaches control of flow rate using a control algorithm that temporarily reverses the flow to overcome vessel collapse. However, none of these methods and apparati uses a single access to the vascular system to perform recirculation. Moreover, none of these provide relief of the vacuum causing the vessel collapse by a shunt to a reservoir before reversing the flow or use a second pump to provide blood flow to open the collapse.
U.S. Pat. No. 6,485,450 teaches infusion of chilled blood or medical fluid and collection of blood for recirculation. This method however, relies on passive collection of blood rather than withdrawal, and this collection is done via separate vascular accesses. None of the references describes cooling the brain by using cold blood flowing to the brain due to cardiopulmonary resuscitation.